Ultra high frequency tuner



A. H. TURNER ULTRA HIGH FREQUENCY TUNER Oct. 8, 1946.

2 Sheets-Sheet 1 Filed March 31, 1943 lllulullllllnllllltllllliliilltllllllllllllil I!!! lrlwllllllllllllllrl ||.L

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ULTRA HIGH FRE uEficY TUNER Filed March 31, l943 2 Sheets-Sheet 2 3noentor Patented Oct. 8, 1946 ULTRA HIGH FREQUENCY TUNER Alfred H. Turner, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 31, 1943, Serial No. 481,215

12 Claims. 1

This invention relates generally to ultra high frequency apparatus and particularly to an improved apparatus for tuning efliciently over a relatively wide band of ultra high frequencies.

One of the conventional methods of tuning at ultra high frequencies is to employ a resonant line of suitable design across one end of which is connected a variable capacitor having a relatively high maximum capacity. Such an arrangement provides a theoretical limit of 1 to 2 between minimum and maximum frequency adjustments. In practice, the theoretical limit is not attainable because of distributed resistances and impedances throughout the circuit. In addition, the loading efiect of the device to which the tuner is connected reduces the practicable tuning frequency band.

The instant invention contemplates the use of a resonant line connected at one end to a suitable utilization circuit. The opposite ends of the line are connected together through one or more variable capacitors and an inductive element having an inductance of the order of that of one of the lines. The resulting circuit comprises a parallel-tuned circuit including the utilization device and the resonant lines, having a series-tuned circuit including the capacitive and the inductive element connected across the ends of the lines remote from the utilization device. Adjustment of the capacitive reactance of the series capacitors therefore effectively provides simultaneous adjustment of both the capacitive and inductive reactances of the circuit. Such an arrangement provides a theoretical limit of one to three between the minimum and maximum tuning frequency limits. Of course, the theoretical limit may not be attainable in actual practice, but the practical limits substantially exceed those possible with the conventional tuning arrangement described heretofore.

Two modifications of this novel and fficient tuning system will be described in detail hereinafter. One means comprises a pair of resonant lines of the order of one quarter to one half wave length at the operating frequency which terminate at one end in the utilization device and at the other end in fixed capacitor electrodes. Two movable capacitor electrodes aredisposed in variable capacitive relation to separate ones of the fixed capacitive elements and arranged to vary simultaneously the capacity between each fixed and movable electrode. A lumped inductive element, such as, for example, a relatively small helix is connected directly between the movable capacitive elements, and may be arranged to rotate with them. The effective inductance of the inductive element is of the order of that employed for one of the resonant lines. It should be understood that two or more tuning units of the type described may be connected to difierent utilization circuits, such as, for example, the input and output circuits of the same or diiierent thermionic tubes. It should also be understood that the rotating capacitive elements may be suitably ganged by means of any convenient mechanical arrangement.

The second modification of the invention to be described in detail hereinafter comprises a concentric line section of the order of one half wave length at the operating frequency, having one end of each of the conductors connected to the utilization device. 'The center conductor of the concentric line is interrupted at a point of the order of one half of the shortest operating Wave length from the end connected to the utilization circuit. The remaining quarter wave section includes at its extremity remote from the utilization circuit a conductive element in close capacitive relation with the other concentric conductor. This conductive element and the inner conductor portion connected thereto is provided with a suitable control element such as, for example, a shaft and a control knob, whereby the gap between the :two portions of the center conductor may be varied to provide a variable series capacitor between said portions. It will be understood that the capacitance between the conductive element which terminates the inner con-, ductor portion and the outer line conductor will remain substantially constant as the capacitance between the inner line portions is varied. Varying the capacitance between the portions of the inner line will vary effectively the capacitive coupling between the quarter wave line connected to the utilization device and the quarter wave line remote therefrom. In operation, the effect is similar to that described for the first modification of the invention, since the effective result is to simultaneously vary the series inductive and capacitive reactance of the circuit.

Among the objects of the invention are to provide an improved method of and means for tuning an ultra high frequency circuit. Another object is to provide an improved method of and means for varying simultaneously the inductive and capacitive reactance of an ultra high frequency circuit. A further object of the invention is to provide an improved method of and means for tuning an ultra high frequency circuit over a relatively wide band of frequencies. Another obiect is to provide an improved method of and means for varying simultaneously the series inductive and capacitive reactance in a plurality of ultra high frequency tuned circuits. A still further object of the invention is to provide an improved method of and means for tuning a concentric ultra high frequency line by adjusting simultaneously the series inductive and capacitive reactances connected to said line.

The invention will be described in greater detail by reference to the accompanying drawings of which Figure 1 is a schematic circuit diagram thereof; Figures 2 and 3 are cross-sectional views of one embodiment thereof; Figure 4 is a schematic circuit diagram of a second embodiment thereof and Figure 5 is an elevational view of the tuning elements illustrated in Figure 4. Figure 5 includes a fragmentary cross-sectional portion to illustrate better the construction thereof. Similar reference numerals are applied to similar elements throughout the drawings.

Referring to Figure 1, a utilization circuit comprising the anode circuits of tubes I and 2, and having an inherent capacitance 3, is connected to one end of a first resonant line represented by an inductance 4 and to one end of a second reso'nant line repreesnted by a second inductance 5. The remaining terminals of the lines 4 and 5 termi'n'ate respectively in fixed capacitive elements 5 and I. A first movable capacitive element 8 is disposed in variable capacitive relation with the first fixed capacitive element 6. A second movable capacitive element 9 is disposed in similar variable capacitive relation to the second fixed capacitive element 1. A third inductive element I0, which, for example, may be a small substantially rigid helix, having an inductance of the order of the inductance of one of the resonant lines, is connected between the first and second movable capacitive elements 8 and 9. The third inductive element 10 may, if desired, be rotated simultaneously with the movable capacitive elements 8 and 9, these movable elementsmay be individually or interdependently rotated.

Referring to Figures 2 and 3, there is provided an arrangement employing a concentric line to replace the lines 4 and 5 of Figure 1. The device includes an inner conductor 4, surrounded by a concentrically disposed outer cylindrical conductor-5, both connected to a utilization device such as a tube H5. The length of the inner conductor 4 is of the order of one half wave length at the highest operating frequency, while that of the outer conductor 5 is substantially greater than three quarter wave length at the highest operating frequency. A second inner conductor H] includes a conductive element II which provides close capacitive coupling between the second inner conductor [0 and the outer conductor 5. This coupling may be maintained substantially constant by means of an insulated ring [2 forming a spacer between the conductive element H and the outer conductor 5. The two inner conductors 4 and ID are disposed coaxially and separated by a gap I3. The width of the gap l3 may be increased or decreased by moving the second inner conductor l0, and the conductive element H attached thereto, axially within the outer conductor 5.

Such movement might be facilitated by means of a control shaft I4 connected to the conductive element l l coaxially with the inner conductor Ill. The control shaft l4 may include a control knob l5 attached thereto. The effective length of the second inner conductor l0 should also be slightly less than one quarter wave length at the highest operating frequency. Moving the second inner conductor l0 axially with respect to the first inner conductor 4 will vary the capacitive coupling between the inner conductors, thereby effectively varying the series capacitive and inductive reactances in the circuit, as explained heretofore. It should be understood that any suitable mechanical arrangement may be provided for moving the control shaft I4 axially with respect to the inner conductor 4.

Referring to Figure 4, an ultra high frequency circuit comprising an ultra high frequency amplifier, an ultra high frequency oscillator and an ultra high frequency mixer or first detector, is shown in combination with tuning circuits of the general type illustrated in Figure 1 and described in detail heretofore. A concentric transmission line 2| connected to, for example, a suitable receiving antenna, not shown, is connected to one end of an input coupling loop 22. The remaining end of the input coupling loop 22 is connected to ground through a variable tuning capacitor 23.

An ultra high frequency balanced amplifier such as, for example, a double pentode tube 24, is self-biased by means of a conventional cathode resistor 25 and cathode bypass capacitor 28 which are connected between the cathode and ground. The control grids of each of the tube pentode sections are connected to the ends of separate ones of a first pair of resonant lines 4, 5 which are of the order of one quarter to one half wave length at the operating frequency. The remaining ends of the resonant lines 4 and 5 terminate respectively in first and second fixed capacitive elements 6 and 1. A grounded center-tapped resistor network 21, 28 is connected between the fixed capacitive elements 6, 1 to provide a D.-C. grid return circuit.

The movable capacitive elements 8 and 9, which are in capacitive relation respectively with the fixed capacitive elements 6, and I, are connected together through a compact bunched inductive element I'D of the type described heretofore. The screen electrodes of the two pentodes of the tube 24 are connected together and bypassed to ground by means of a screen capacitor 29. Operating potentials for the screen electrodes and the anodes of the two pentodes are provided from any suitable source, not shown, and applied to the respective electrodes through suitable isolating resistors 30, 3| and 32.

The anodes of the two pentodes are each connected to one end of a second pair of resonant lines 34, 35 terminate in a similar tuning unit 5, 1, 8', 9, l0. In order to match the two tuned circuits, a matching capacitor 33 may be connected between the anode terminals of the lines 34, 35. Similarly, separate fixed capacitors 0 may be connected selectively by means of switches 8, across each group of resonant lines adjacent the utilization circuits connected thereto, to provide a tuner having a plurality of tuning frequency ranges.

Suitable coupling between the input loop 22 and either of the first resonant lines 4, 5 may be provided by spacing the conductors to provide desired mutual inductance between them. A shield 36 preferably surrounds all of the app'aratus described heretofore. A second shield 31 separates the first resonant lines 4, 5, and their associated tuning unit, from the second resonant lines 34, 35 and their associated tuning unit,

V respectively. I

"triode 44 having the two anodes thereof-peonnected together and to the primary of an intermediate frequencytransformer, not shown. The cathode is connected to ground through a conventional self-biasing circuit including a cathode resistor 45 and a parallel connected capacitor 46. The control electrodes of the two triodes are each connected to one end of separate resonant lines 41, 48 which are mutually coupled to the second resonant lines 34, 35 througha suitable aperture in the shield 36. The third resonant lines 41, 48 are tuned by a third tuning unit 6", l", 8", 9f, I07, of the type described heretofore. A grounded center-tapped resistor network 49, 58 is connected between the fixed capacitive elements 6", I? toprovide a D.C. grid return circuit for the balanced converter.

I An ultra high frequency oscillator includes a double triode 54 having its cathode connected to ground through a cathode resistor 55 and cathode capacitor 55. The grid circuit of the oscillator is comprised of a, loop of copper foil terminating in the two control electrodes and having its center-point grounded through a grid resistor 51. The anode circuit of the push-pull oscillator includes a fourth pair of resonant lines 58, 59 and a fourth tuning unit 6", 1, 8, 9" and lil'. Anode potential is applied to the two anodes through anode resistor 52, 53.

The four tuning units described heretofore may be ganged as indicated by the dash lines 60. The balanced oscillator circuit may be coupled to the converter input circuit by means of mutual coupling between the lines 48 and 58 through a suitable aperture in a third shield 38 which separates the oscillator from the converter. t should be understood that the constants of the circuitwill be so selected that the desired intermediate frequency may be derived from the converter anode circuit.

For example, the several tuning capacitors may be of a conventional type providing a capacity range of the order of from one to ten micromicro-farads. As explained heretofore, the

length of the various resonant lines is selected to be of the order of one-quarter to one-half wave length at the operating frequency. Circuits of the type described have been constructed to provide suitable tuning over ranges extending from 250 to 400 megacycles and 400 to 600 megacycles. This range could be extended readily by proper selection of circuit constants.

Referring to Figure 5, the constructional details of the circuit schematically described in Figure 4 indicate one satisfactory arrangement of this apparatus. A single tuning knob Bl attached to a single insulated tuning shaft 63 controls the rotation of all of the movable capacitive elements 8, 8, 8", 8 and 9, 9', 9", 9". entire assembly is enclosed in a suitable outer shield 65. Only the connections and apparatus corresponding to the ultra high frequency tuner are shown in order to simplify the comparison of the structural and schematic layouts of Figures 4 and 5. All elements are identified with the same reference numerals as corresponding portions of Figure 4.

It should be understood that all of the switches 8 may be opened and closed synchronously by any suitable motor drive, and that the several tuning units may be similarly adjusted synchronously, to provide a scanning type tuner. Also the oscillator described may be utilized as a transmitter, and the switch s, the tuning capacitor or the tuning unit thereof, or any of them may be ad- The justedby-a suitable motor drive to provide-a fjamming transmitter. p Thustheinvention described comprises several modifications of a novel and efficient tuner for a, relatively wide band of ultra high frequencies including means for adapting the tuner to operation in an ultra high frequency superheterodyne amplifier-oscillator-converter circuit.

I claim as my invention: 1. An ultra high frequency tuning circuit including a pair of inductive elements, at least one adjustable capacitiveelement, a third inductive element having an inductance at least of the order of the inductance ,of one of said pair of elements and movable with said capacitive element, a utilization device, means connecting one terminal of each of said pair of inductive elements to saidutilization device, means connecting the remaining terminals of said pair of elements in series relation with said capacitive element and said third inductive element, and

means for adjusting said capacitive element-to vary simultaneously the effective series inductive and capacitive reactance of said circuit.

2. An ultra high frequency tuning circuit including a pair of inductive elements, a pair of adjustable capacitive elements each having at least a fixed electrode and a movable electrode, a third inductive element having an inductance at least of the order of the inductance of one of said pair of elements, means connecting and supporting said third inductive element between said movable electrodes of said capacitive elements so that said third inductive element is movable with said movable electrodes, means connecting 'one extremity of each of said elements of said pair to a different one of said fixed electrodes of said-capacitive elements, a utilization device, means connecting the remaining ends of said pair of elements to said utilization device, and means for adjusting simultaneously the capacity of said capacitive elements to vary simultaneously the effective series inductive and capacitive reactance of said circuit. 3; A plurality of circuits of the type described in claim'2 including means for adjusting simultaneouslyall of said capacitive elements, and means for coupling together at least two of said circuits.

4. A plurality of circuits of the type described in claim 2 including means for adjusting simultaneously all of said capacitive elements, and inductive means for coupling together at least two of said circuits.

5. Apparatus of the type described in claim 2 including a tuning capacitor, and means connecting said tuning capacitor between said pair of elements adjacent said utilization device.

6. A plurality of circuits described in claim 2 including means for adjusting simultaneously all of said capacitive elements, means for coupling together at least two of said circuits, a plurality of tuning capacitors, and means connecting each of said tuning capacitors between said pair of elements adjacent each of said utilization devices.

7. An ultra high frequency tuning circuit including a resonant section of concentric transmission line having an inner conductor coaxially disposed with respect to an outer cylindrical conductor, said conductor being discontinuous forming a capacitive gap between the portions thereof, conductive means connected to the extremity of one of said portions of said inner conductor remote from said gap in close capacitive relation with said outer conductor; a utilization device, means connecting the extremity of said outer conductor and the extremity of saidinner conductor portion both remote from Saar conductive means and said capacitive gap to said utilization device, and means for adjusting the length of said capacitive gap between the portions of said inner conductor tovary simultaneously the effective series inductive and capacitive reactance of said circuit.

8. An ultra high frequency tuning circuit including' a resonant section of concentric transmission line having an inner conductor coaxially disposed with respect to an outer cylindrical conductor, said conductor being discontinuous forming a capacitive gap between the portions thereof, conductive means connected to the extremity or one of said portions of said inner conductor remote from said gap in close capacitive relation with said outer conductor, a utilization device; means connecting the extremity of said outer conductor and the extremity of said inner conductor portion both remote from said conductive means and said capacitive gap to said utilization device, and means operable efiectively coaxially with said line for adjusting the length of said capacitive gap between the portions of said inner conductor to vary simultaneously the effective series inductive and capacitive reactance of said circuit.

9. An ultra high frequency tuning circuit including a pair of inductive elements, a pair of adjustable capacitive elements each having at least a. fixed electrode and a movable electrode, a third inductive element, means connecting and supporting said third inductive element between said: movable electrodes of said capacitive elements so that said third inductive element is movable with said movable electrodes, means connecting one extremity of each of said elements of said pair of inductive elements to a different one of said fixed electrodes of said capacitive elements, a utilization device including an input circuit and an output circuit, means connecting the remaining ends of said pair of elements to one of said circuits of said utilization device, and means for adjusting simultaneously the capacity of saidcapacitive elements to vary simultaneously the" eflectiv'eseries inductive and capacitive reactance of said circuit.

10. A plurality of circuits of the type described in claim 9' including means for adjusting simultaneously all of said capacitive elements, and means for coupling together at least two of said circuits.

11. An ultra high frequency tuning circuit including a pair of inductive elements, a pair of adjustable capacitive elements eachhaving at least a fixed electrode and a movable electrode, a third inductive element having an effective inductance of the order of the inductance of one of said pair of elements, means connecting and supporting said'third inductive element between said movable electrodes of said capacitive elements so that said third inductive element is movable with said movable electrodes, means connecting one extremity of each of said elements of said pair to a different one of said fixed electrodes of said capacitive elements, a utilization device,- means connecting the remaining ends of said pair of elements to said utilization device, and means for adjusting simultaneously the capacity of said capacitive elements to vary simultaneously the effective series inductive and capacitive reactance of said circuit.

12. An ultra high frequency tuning circuit including a resonant section of concentric transmission line having an inner conductor coaxially disposed with respect to an outer cylindrical conductor, said conductor being discontinuous forming a capacitive gap between portions thereof, conductive means connected to the extremity of one of said portions of said inner conductor remote from saidgap in close capacitive relation with said outer conductor, a utilization device, means connecting the extremity of said outer conductor and the extremity of said inner conductor portion remote from said conductive means and said capacitive gap to said utilization device, and means for adjusting the length of said capacitive gap between the portions of said inner conductor to vary simultaneously the effective series inductive and capacitive reactance of said circuit.

ALFRED H. TURNER. 

